To support utility lines, for example, 345 KV power lines, it is conventional to use single pole structures, Y structures, H frame structures, and/or lattice steel towers.
Conventional utility line support structures may be made of tubular metal sections, wood, angle iron, or concrete. The concrete may be solid or tubular, and may be reinforced, post-tensioned, or pre-stressed.
Many conventional Y structures and H frame structures are made of tubular pole sections. Tubular pole sections are expensive. Not only are the tubular poles themselves expensive, but the connecting boxes between tubular stems and arms are also expensive because they terminate a stem tube section with a square section in order to make a bolted connection with a square section that terminates the tube section of the arms.
One reason that closed sections such as tubes are expensive is because welding adjacent tube sections together to make a long pole requires using circumference welds that are difficult to make and require careful inspection and a high degree of quality control.
However, a closed section is desirable in utility line supports because it has a great deal of strength and torsional stability.
On the other hand, an open section, such as a channel, is easier and less expensive to manufacture, and is easier to work with in the field when installing it to form utility line support structures. Also, channel sections are easy to butt weld together with easily inspected welds.
In a Y support structure, it is a problem to connect a tubular stem or column to tubular Y arms. It is conventional to make the connection by using an expensive bolted connection in the form of a shaped box made from flat plate.
Tubular steel poles compete with wooden poles as support structures for utility lines. While tubular steel poles are comparatively more expensive than wooden poles, tubular steel poles cost less to erect than the wooden ones.
Lattice steel towers are also used to support utility lines and are expensive to erect due to the many pieces and also because they require four foundations precisely placed with respect to each other. Moreover, lattice steel towers are very rigid and do not deflect under load. If something happens to a utility line to suddenly increase the load, such as a wire breaking or ice falling off of one span but not the other, the tower either supports the load or it fails. On the other hand, tubular support structures have the advantage of deflecting when subjected to an increased load, thereby reducing the imbalance and the possibility of their falling down.
In at least one instance, 60 miles of power line and its supporting lattice steel towers cascaded down, one after the other, because the rigid towers could not deflect and withstand the increased load.
The various rolled shapes available as structural elements for utility line support structures, such as a rolled "I" beams and channels, have not been acceptable to the utility companies because they are not economical or efficient from a strength viewpoint. Accordingly, there is a need for a utility line support structure that is economical and has a high strength to weight ratio.
Acknowledgement is made of the following prior art patents: U.S. Pat. Nos. 709,554; 1,877,583; 2,066,419; 2,136,122; 3,034,209; 3,054,482; 2,659,270; 3,713,262; French Pat. No. 673,690; 747,235; 801,895; British Pat. No. 263,116.